LOL… computers are pretty hearty guys, and the ‘on or off’ issue really only boils down to two things: Your power consumption / conservation habits or needs, and care and upkeep of your machine. If you want to save power, turn it off. If not, leave it on but set the power configurations for when it’s not in use (to sleep / hibernate). Other than that, if you take good care of your machine, make sure the CPU, etc gets the proper cooling, ventilation and the guts get dusted now and then, you’re fine either way.
And remember, computers rarely die of old age from turning them off and on too much, or not turning them off often enough. (Unless you constantly flip back and forth multiple times every single day). Most computers die from other causes, faulty power supplies, bad capacitors, fried CPUs, bad motherboards, broken fans, dropped or knocked over, animal attacks, spilled energy drinks, etc etc.
And after all, just consider servers…... Hey Fluther sysadmins, when was the last time you turned off your web servers? LOL